Mutations of one copy of the BRCA2 gene predisposes humans to breast cancer (Wooster et al., Nature, 1995. 378:789-792, Tavtigian et al., Nat. Genetic, 1996. 12:333-337). Breast tumors from predisposed individuals often display mutations in both alleles suggesting that BRCA2 serves as a tumor suppressor (Collins et al., Oncogene 1995. 10:1673-1675, Gudmundson et al., Cancer Research 1995. 55:4830-4832). In addition, deleterious alleles of BRCA1 and BRCA2 are responsible for almost all familial ovarian cancer, and deleterious alleles of BRCA2 are also involved in hereditary male breast cancer (Wooster et al., 1995, Tavtigian et al., Nat. Genetic, 1996. 12:333-337, Miki et al., Science 1994. 266:66-71). BRCA2 encodes a large protein of about 390 kDa which does not possess any obvious homology with sequences available in the public database (Tavtigian et al., Nat. Genetic, 1996. 12:333-337).
Recently, in vitro transactivation assays have suggested a role for the amino-terminal domain of BRCA2 in transcriptional regulation (Milner et al., Nature 1997. 386: 772-773). However, most of the current data point to a role for the BRCA2 protein in DNA repair. It has been reported that the BRCA2 protein interacts with RAD51 (Marmorstein et al., Natl. Acad Sci. 1998. USA 95: 13869-13874, Chen et al., Proc. Natl. Acad. Sci. 1998. USA 95: 5287-5292, Mizuta et al., Proc. Natl. Acad. Sci. 1997. USA 94: 6927-6932), the human homolog of Escherichia coli recA (Shinohara et al., Cell 1992. 69:457-470). RAD51 is the hallmark of homologous recombination, suggesting a function for BRCA2 in recombination or double-strand break DNA repair. It has also been shown that murine embryos with a targeted disruption of BRCA2 displayed sensitivity to ionizing radiation (Sharan et al., Nature 1997. 386:804-810). Mouse embryo fibroblasts (MEFs) with a targeted disruption of BRCA2 exon 11 displayed increased sensitivity to ultraviolet light and methyl methanesulfonate (MMS) (Patel et al., Mol. Cell, 1998. 1:347-357).
To determine the role for the BRCA2 protein in cancer predisposition, attempts have been made to analyze the induction of tumors in mice with a targeted deletion in BRCA2. However, contrary to expectations, mouse strains heterozygous for mutations in BRCA2 failed to show a predisposition to tumor formation (Ludwig et al., Genes Dev., 1997. 11:1226-1241, Sharan et al., Nature, 1997. 386:804-810, Suzuki et al., Genes Dev., 1997. 11:1242-1252, Connor et al., Nat. Genet., 1997. 17:423-430). Homozygosity caused early embryonic lethality at day 7.5-8.5 and was accompanied by retarded embryonic growth in vivo and in vitro (Ludwig et al., Genes Dev., 1997. 11:1226-1241, Sharan et al., Nature, 1997. 386:804-810, Suzuki et al., Genes Dev., 1997. 11:1242-1252). Embryonic survival was prolonged to day 10.5 when the analysis was performed with BRCA2 homozygous mouse with a p53-null background (Ludwig et al., Genes Dev., 1997. 11:1226-1241). It has also been shown that some animals with a homozygous deletion of exon 11 survive to maturity and succumb to thymic lymphomas (Friedman et al., Cancer Research, 1998. 58:1338-1343). Human BRCA2 exon 11 is composed of eight internal repeats known as the “BRC repeats” that are conserved in all mammalian BRCA2 proteins that have been sequenced (Koonin et al., Nat. Genet., 1996. 13:266-268, Bork et al., Nat. Genet., 1996. 13:22-23).